Electric discharge apparatus



Aug. 23, 1938. E. F. LOWRY 2,123,051

ELECTRIC DISCHARGE APPARATUS i Original Filed Oct. 5. 1935 WITNESSES:INVENTOR gErwin E Low/y.

Patented A 23, 193s UNITED STATES ELECTRIC DISCHARGE APPARATUS Erwin F.Lowry, Batavia, 111., assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania Originalapplication October 3, 1935, Serial No. 43,347. Divided and thisapplication August 26, 1936, Serial No. 97,979 i 6 Claims.

This application is a division of my copending application Serial No.43,347, filed October 3, 1935, for Electric discharge apparatus.Myinvention relatesto electric discharge ep- 5 paratus and it hasparticular relation to lamps utilizing heated electrodes operating in agaseous atmosphere.

One common type of lamp to which the application of the-inventionpertains is one having similar electrodes coated with a mixture ofalkaline earth metal oxides. These similar electrodes are heated andelectrons are emitted by the coating. Alternating current is applied tothe two electrodes anda discharge takes place through thegaseous mediumwith first one electrode acting as a cathode and the otheran anode andthen vice versa. The gaseous medium used is commonly mercury vapor andthe ionization of this vapor by the discharge produces a spec- 50 trumthat is rich in ultra-violet light. These lamps are accordingly ratherwidely used for the beneficial use of this ultra-violetlight.

In these gaseous discharge lamps, however, the electrons emittedby theelectrode acting as a cathode react -,on the gaseous or vapor medium inwhich the electrodes are immersed to produce I positiveions which drifttowards this electrode acting as a cathode under the action of theelectromotive 'force impressed between the two elecv trodes. When thiscathode electrode is heated to the proper temperature, suillcientelectrons are emitted from its surface to protect the coating from theeffects of the positive ions which are drawn thereto. If, however, thecathode elec- 35 trode is not heated to a sufliciently high temperatureat the same time apotential difference is impressed between the twoelectrodes, the positive ions-impingingon the cathode attack theemissive coating. In addition, the are which is produced under theaction of the potential between the electrodes has a comparatively highpotential drop by reason of thescarcity of electrons emitted from thecathode electrode. Under such circumstances, hot spots tend to form on45 the surface of the cathode with the result that considerable portionsof the active coating are stripped.

customarily, the discharge lamp devices of the type involved here areprovided with electrodes 50 which mustbe heated for a considerableinterval of time before they are safe from positive ion bombardment. Asthe cui'rent output for which the discharge device is providedincreases, the size of the cathode increases and the time required forheating the electrode to the properv temperature correspondinglyincreases. The necessary time may vary from five seconds'toapproximately five minutes or more.

-It is an object of my invention to provide a lamp discharge device ofthe ,hot electrode gas or vapor filled type in which the electrodesshall be protected from damage thereto arising when the potentialbetween the electrodes causes a discharge prior to the time that theelectrodes,

reach a temperature at which their emission equals or exceeds themaximum current through the device.

Another object of my invention is to protect the electrodes from thedeleterious effects of premature discharge between the electrodes.

Another object of my invention is to provide an illuminating unit of theglow discharge type that shall be capable of continuous operation over along interval of time.

According to my invention, the lamp discharge device is provided withscreening members or shields which completely. enclose the electrodes.The shield is so constructed that electrons from the electrode acting asa cathode may be transmitted through its surface. This object isaccomplished either by providing the shield with one or moreperforations or by constructing the shield of such thin material that itis punctured by the electrons from the emissive electrode as they moveunder the influence of the potential between the electrodes. Theinterior surface of the shield is designed to be thermionically active.However, I have found that the shield, while it may he, need not becoated before it is mounted in the discharge device. An uncoated shieldmay be mounted adjacent to the electrodes. After the electrodes haveoperated for a short interval of time, sufllcient coating material isprojected from the cathode onto the shield to render the interiorsurface, of the latter emissive. I

The shield is connected in circuit with the electrode in such mannerthat when the electrode is below the proper temperature for emission,the shield operates as a blocking control electrode. It is, moreover,disposed in such proximity to the electrode that it is heated thereby.'As the temperature of the electrode rises, that of the shield alsorises and a.continuously increasing stream of electrons is emitted fromtheinteriorcharge layer. This .type of electron emission has beendesignated as a threshhold discharge. This emission will createionization in the gaseous medium, and when the'emission reaches acertain state, the electrons will break through the space charge on theshield and a discharge will occur between the electrodes. The length oftime necessary to heat the shield to permit the, discharge of electronsthrough the insulating space charge layer automatically creates a timelag that protects the electrodes from a premature establishment of thedischarge between the electrodes.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of the specificembodiments when read in connection with the accompanying drawing, inwhich:

The figure is a view in section showing a glow discharge lampconstructed in accordance with my invention.

The lamp comprises an envelope I9 through a reentrant portion 14 ofwhich rods 15 project. A plurality of heating elements 11 suitablysupported on rods 15 are disposed within theenvelope. Each filamentaryelement 11 is enclosed within a tube 19 having disks 8| of ceramic orother insulating material at the ends and emissive walls 83 extendingbetween the ends. The

- disks 8| are provided with shoulders 85 and 81 and the emissive walls88 are supported between the innermost shoulders 88 of each set ofdisks.

On intermediate shoulders, of the disks, screening members 89 aresupported. .The screening members 89 are preferably composed ofperforated sheetv cylinders although wire mesh may also be used.Connectors 9| are welded to each I of the perforated cylinders or wiremeshes 89 and to the rods 15 to co ect the screening member 89 and theemitting ectrodes. Similar conductors 99-are welded to the emissivewalls 88 and the rods 15. The filamentary elements 11 are each welded toa short rod 95 at the top. The

' rods 95 project through the ceramic disks 8| and are-welded'to acrosspiece 91. The cross piece 91 thus connects the emissive electrodes inseries with each other. To support each of the assemblies TI, 19, 89 anupright member 99 sealed in the stem I4 and welded to. the crossplece.9l at the center is provided. To provide the necessary vaporatmosphere, a globule of mercury llll is disposed within the envelope.

Power is supplied to the lamp by connecting the leads 15 .to a source ofalternating current.

The current heats the :filaments I1, which are preferably of an alloycomprised of nickel, cobait" and term-titanium. The heat energy radiatedby these filaments heats up the alkaline earth oxide coating on thewalls 89 and produces electrons therefrom. The space charge on theshields'or screen members 89 prevents the passage of electronsthere'through. The heating en-,

ergy is also extended to the shield 89 and gradually heats it to anelectron emitting temperature. The emission of these electrons willreduce the thickness of the insulating space charge layer and this typeof discharge has been desig- The emission nated as a. thresholddischarge. will create ionization in the gaseous medium and willresultin the electrons breaking through the space charge onthe screenmember, and the i Although I have shown and described a certain specificembodiment of my invention, I am fully aware that many modificationsthereof are possible, especially in the number, shape, arrangement andconnections between the various elements. My invention, therefore, isnot to be restricted except insofar as is necessitated by the prior art.

I claim as my invention:

1. In combination, a first electrode to be heated to emit electrons, ashell .completely enclosing said first electrode and having meanstherein to transmit electrons generated in its interior therethrough,said shell to beheated by the heating energy emitted by said firstelectrode and being activated-i'onelectron emission when heated, a

- second electrode to be heated to emit electrons, a

shell completely enclosing said second electrode and-having meanstherein totransmit electrons generated in its interior therethrough,said lastmentioned shell to be heated by the heating energy emitted bysaid secondelectrode and being activated for electron; emission whenheated,

means connecting each of said shells to the emitting electrode that itencloses, a gaseous atmosphere surrounding-said electrodes and shellsand means for impressing a iperiodic potential between said electrodes.3

2; Apparatus according to claim 1, characterized by the fact thatgaseous atmosphere is an atmosphere mercury vapor provided by a globulelocated; near the electrodes.

3. 'An electric discharge device comprising a casing, a gaseousatmosphere therein, electrodes emitting electrons in response to heatingenergy, means for applying heating energy to said electrodes, a memberdisposed adjacent to said emissive electrodes in the path otelectronstherefrom and having openings therethrough, said member when cold havinga space charge blocking the passage of electrons through said openings.said member receiving heating energy from at least one of said electronsemitting electrodes, .said member becoming electron emitting in responseto said received heating energy and havinga time lag betweenits coldelectron blocking condition and its condition of sufilcient electronemission permitting the passage of electronsbetween said electronemitting electrodes.

4; A lamp having a plurality of similar electrodes therein, meansapplying heating energy to said electrodes to emit electrons, a memberdisposed adJaent each of said electrodes inthe path of electronstherefrom and having openlugs therethrough, said members when coldhaving a space charge blocking the passage of elec-.

trons through saidopenings, said members receiving heating energy fromsaid electrodes, said members becoming electron emitting in response tosaid received heating energy-and having a time lag between theircoldelectron blocking condition and their condition of sufllcient electronemission permitting the passage of electrons from one or said electronemitting electrodes to another.

5. An electron discharge gaseous lamp comprising at least two similarelectrodes for receiving an electron, discharge therebetween, aperlorated screen surrounding said electrodes and having a space chargewhen cold preventing the passage of electrons therethrough, means forapplying heating energy to said electrodes, said heating energy adaptedto remove said space a time lag.

charge on said perforated screen after a time lag.

6. n electron discharge gaseous lamp comprising at least two similarelectrodes, a perforated screen between said electrodes preventing, whencold, a discharge between said electrodes, means for applying heatingenergy to "said elec trodes, said heating energy heating said'perforatedscreen and permitting said discharge after ERWINY r'. IOWRY.

